1 /* 2 * RCU segmented callback lists 3 * 4 * This seemingly RCU-private file must be available to SRCU users 5 * because the size of the TREE SRCU srcu_struct structure depends 6 * on these definitions. 7 * 8 * This program is free software; you can redistribute it and/or modify 9 * it under the terms of the GNU General Public License as published by 10 * the Free Software Foundation; either version 2 of the License, or 11 * (at your option) any later version. 12 * 13 * This program is distributed in the hope that it will be useful, 14 * but WITHOUT ANY WARRANTY; without even the implied warranty of 15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 16 * GNU General Public License for more details. 17 * 18 * You should have received a copy of the GNU General Public License 19 * along with this program; if not, you can access it online at 20 * http://www.gnu.org/licenses/gpl-2.0.html. 21 * 22 * Copyright IBM Corporation, 2017 23 * 24 * Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com> 25 */ 26 27 #ifndef __INCLUDE_LINUX_RCU_SEGCBLIST_H 28 #define __INCLUDE_LINUX_RCU_SEGCBLIST_H 29 30 /* Simple unsegmented callback lists. */ 31 struct rcu_cblist { 32 struct rcu_head *head; 33 struct rcu_head **tail; 34 long len; 35 long len_lazy; 36 }; 37 38 #define RCU_CBLIST_INITIALIZER(n) { .head = NULL, .tail = &n.head } 39 40 /* Complicated segmented callback lists. ;-) */ 41 42 /* 43 * Index values for segments in rcu_segcblist structure. 44 * 45 * The segments are as follows: 46 * 47 * [head, *tails[RCU_DONE_TAIL]): 48 * Callbacks whose grace period has elapsed, and thus can be invoked. 49 * [*tails[RCU_DONE_TAIL], *tails[RCU_WAIT_TAIL]): 50 * Callbacks waiting for the current GP from the current CPU's viewpoint. 51 * [*tails[RCU_WAIT_TAIL], *tails[RCU_NEXT_READY_TAIL]): 52 * Callbacks that arrived before the next GP started, again from 53 * the current CPU's viewpoint. These can be handled by the next GP. 54 * [*tails[RCU_NEXT_READY_TAIL], *tails[RCU_NEXT_TAIL]): 55 * Callbacks that might have arrived after the next GP started. 56 * There is some uncertainty as to when a given GP starts and 57 * ends, but a CPU knows the exact times if it is the one starting 58 * or ending the GP. Other CPUs know that the previous GP ends 59 * before the next one starts. 60 * 61 * Note that RCU_WAIT_TAIL cannot be empty unless RCU_NEXT_READY_TAIL is also 62 * empty. 63 * 64 * The ->gp_seq[] array contains the grace-period number at which the 65 * corresponding segment of callbacks will be ready to invoke. A given 66 * element of this array is meaningful only when the corresponding segment 67 * is non-empty, and it is never valid for RCU_DONE_TAIL (whose callbacks 68 * are already ready to invoke) or for RCU_NEXT_TAIL (whose callbacks have 69 * not yet been assigned a grace-period number). 70 */ 71 #define RCU_DONE_TAIL 0 /* Also RCU_WAIT head. */ 72 #define RCU_WAIT_TAIL 1 /* Also RCU_NEXT_READY head. */ 73 #define RCU_NEXT_READY_TAIL 2 /* Also RCU_NEXT head. */ 74 #define RCU_NEXT_TAIL 3 75 #define RCU_CBLIST_NSEGS 4 76 77 struct rcu_segcblist { 78 struct rcu_head *head; 79 struct rcu_head **tails[RCU_CBLIST_NSEGS]; 80 unsigned long gp_seq[RCU_CBLIST_NSEGS]; 81 long len; 82 long len_lazy; 83 }; 84 85 #define RCU_SEGCBLIST_INITIALIZER(n) \ 86 { \ 87 .head = NULL, \ 88 .tails[RCU_DONE_TAIL] = &n.head, \ 89 .tails[RCU_WAIT_TAIL] = &n.head, \ 90 .tails[RCU_NEXT_READY_TAIL] = &n.head, \ 91 .tails[RCU_NEXT_TAIL] = &n.head, \ 92 } 93 94 #endif /* __INCLUDE_LINUX_RCU_SEGCBLIST_H */ 95